A seal assembly for limiting the amount of movement or distortion experienced by a seal element which is retained by a seal housing.
In a typical seal assembly a seal element is retained by a seal housing. The seal element provides a sealing surface which in service may be exposed to a variety of forces acting on the seal which tend to move or distort the seal element. This movement or distortion may result in the seal failing to perform as intended either by permitting leakage across the seal or by allowing abrasive media to become embedded in the sealing surface, thus causing premature wearing of the seal element.
The forces acting on the seal may be caused by a pressure differential across the seal element, in which case the sealing surface will tend to move or distort laterally within the seal housing either so that the sealing force exerted by the sealing surface against its abutting component is reduced or so that the seal element is xe2x80x9cliftedxe2x80x9d out of the seal housing by fluid which passes under pressure between the seal element and the seal housing. These effects becomes more problematic where there is a high constant or transient differential pressure across the seal.
It may be possible to counteract these effects by using springs or other biasing devices to provide additional sealing force to keep the sealing surface engaged with both the abutting component and with the seal housing. Unfortunately, however, the necessary spring force increases with the pressures exerted on both sides of the seal and with the differential pressure across the seal. If the spring force is too high the amount of deformation and compression of the seal element caused by the spring force may itself result in the seal element failing to perform as intended.
Where the seal is a dynamic seal, the forces may also result from movement of components associated with the seal or from relative movement between the sealing surface and components abutting the sealing surface. If the dynamic seal provides a seal between components that move axially relative to each other then the seal element may tend to move axially due to friction in the same direction as the component that abuts the sealing surface. If the dynamic seal provides a seal between components that rotate relative to each other then the seal element may tend to rotate due to friction in the same direction as the component that abuts the sealing surface.
Regardless of whether the movement or distortion of the seal element is caused by differential pressure or relative movement of components, it may be controlled by providing one or more engagement forces between the seal element and the seal housing during service which restrain the seal element against movement in the seal housing.
The engagement force or forces between the seal element and the seal housing during service may be achieved by permanently fixing the seal element in the seal housing by gluing or otherwise connecting the seal element with the seal housing. Unfortunately this option may result in higher fabrication costs by complicating the design of the seal and may also increase the difficulty of replacing seal elements as they become worn.
There is therefore a need for a seal assembly in which movement or distortion of the seal element can be limited by providing one or more engagement forces between the seal element and the seal housing during service without permanently fixing the seal element in the seal housing and without relying exclusively on springs or other external mechanisms for supplying an effective engagement force.
The present invention is an improvement in a seal assembly of the type comprising a seal element and a seal housing, which seal assembly is useful for limiting the movement of the seal element in the seal housing. The improved seal assembly limits movement of the seal element in the seal housing by providing one or more engagement forces between the seal element and the seal housing during service without having to permanently fix the seal element in the seal housing.
The seal assembly derives the engagement force between the seal element and the seal housing from pressure which may exerted on the seal element during service, which engagement force in turn results in a frictional force which serves to restrain the seal element from movement in the seal housing. The engagement force is provided by reducing the extent to which pressurized fluid is allowed to be present throughout the interfaces between the seal element and the seal housing.
The presence of pressurized fluid throughout the interfaces between the seal element and the seal housing is reduced by providing that one of the seal element and the seal housing is comprised of a compressible material and by providing one or more gaps between a seal engagement surface on the seal element and a housing engagement surface on the seal housing.
This gap provides an isolated space into which the compressible material of the seal element or seal housing may be pressed under the influence of pressure acting on the seal element in order to provide the engagement force between the seal element and the seal housing. An advantage of the invention is that the magnitude of the engagement force increases as the pressure acting on the seal element increases.
In a preferred aspect, the invention is an improvement in a seal assembly comprising a seal element retained by a seal housing, wherein one of the seal element and the seal housing is comprised of a compressible material, wherein the seal element is comprised of a seal engagement surface, and wherein the seal housing is comprised of a housing engagement surface for engaging the seal engagement surface, the improvement comprising at least one of the seal engagement surface and the housing engagement surface defining a depression for providing an isolated gap between the seal engagement surface and the housing engagement surface.
Either of the seal element or the seal housing may be comprised of a compressible material. For example, the seal assembly may be comprised of a compressible seal element retained by a rigid seal housing or the seal assembly may be comprised of a rigid seal element retained by a compressible seal housing. In the preferred embodiment the seal assembly is comprised of a compressible seal element retained by a rigid seal housing.
The compressible material may be comprised of a non-resilient compressible material which does not return to its original shape when pressure is removed from it, although the use of non-resilient compressible materials may necessitate replacement of the compressible seal element or the compressible housing element, as the case may be, each time the seal assembly is exposed to a cycle of pressurization and depressurization. Preferably the compressible material is therefore comprised of a resilient compressible material which can be reused following decompression.
The depression may be defined by the seal engagement surface, the housing engagement surface, or by both the seal engagement surface and the housing engagement surface. Preferably the depression is not defined by a surface which is comprised of a compressible material in order to limit any distorting effect on the depression which may be caused by pressure between the seal engagement surface and the housing engagement surface. In the preferred embodiment where the seal element is comprised of a compressible material the depression is preferably defined by the housing engagement surface.
The seal assembly may be a static seal assembly or a dynamic seal assembly. In the preferred embodiment the seal assembly is a dynamic seal assembly in which a component such as a rotating shaft abuts a sealing surface of the seal element.
Each of the seal element and the seal housing may be comprised of one or more engagement surfaces. Typically the seal assembly will provide for a plurality of seal engagement surfaces which engage a plurality of housing engagement surfaces in order that the seal element is retained by the seal housing. Some or all of the pairs of engagement surfaces may be oriented in different planes. Depressions may be associated with one or more of these pairs of engagement surfaces to provide for one or more engagement forces, which engagement forces may thus be exerted in one or more directions. The engagement surfaces may be circumferential surfaces which surround the component which abuts the sealing surface of the sealing element.
In the preferred embodiment, the seal element and the seal housing are each comprised of a plurality of engagement surfaces but a depression is defined in only one pair of engagement surfaces. In the preferred embodiment the depression is defined by a housing engagement surface which is oriented in a plane normal to the longitudinal axis of the shaft which rotates within the seal assembly. In the preferred embodiment the seal engagement surface and the housing engagement surface are circumferential surfaces which surround a rotatable shaft which abuts the sealing surface of the sealing element.
The depression may be comprised of any shape or configuration which is capable of providing an isolated gap between the seal engagement surface and the housing engagement surface. An isolated gap is necessary in order to inhibit the passage of pressurized fluid into the gap which may offset or neutralize the engagement force otherwise exerted between the seal engagement surface and the housing engagement surface.
The depression may be comprised of a single isolated depression or may be comprised of a depression pattern. Preferably the depression is comprised of a depression pattern. Preferably the depression pattern is distributed throughout a substantial portion of the seal engagement surface or the housing engagement surface so that the engagement force is likewise distributed.
The depression pattern may be comprised of one or more grooves. In the preferred embodiment where the seal engagement surface and the housing engagement surface are comprised of circumferential surfaces the depression pattern may be comprised of a single uninterrupted groove (such as a semi-circular, circular or spiral groove) or may be comprised of a plurality of unconnected grooves which extend along the seal engagement surface or the housing engagement surface, as the case may be. Preferably the groove or grooves extend in a direction perpendicular to the longitudinal axis of the rotating shaft but they could also extend in a direction parallel to the longitudinal axis of the rotating shaft.
In the preferred embodiment the depression pattern is comprised of a plurality of unconnected substantially parallel grooves which extend circumferentially around the housing engagement surface concentrically in a direction perpendicular to the longitudinal axis of the rotating shaft.
The depression pattern may also be comprised of a plurality of dimples in the housing engagement surface. The dimples may be of any shape, size or configuration as long as they provide the necessary depression and thus gap in the seal engagement surface or the housing engagement surface, as the case may be.
The depression or depression pattern forms a depression profile in the seal engagement surface or the housing engagement surface, as the case may be. The depression profile may comprise any shape. For example, the depression profile may be a bevelled surface, a rounded surface or may be a truncated bevelled or rounded surface.
The seal assembly preferably includes a preloading mechanism for applying a preloading force to urge the seal engagement surface and the housing engagement surface into engagement with each other. The purpose of this preloading force is to provide an initial engagement force between the seal engagement surface and the housing engagement surface to inhibit the passage of fluid between the engagement surfaces in order to enable the engagement force to develop in the depression as the pressure applied to the seal element increases while the seal assembly is in service.
The preloading mechanism may be comprised of any apparatus or device that is capable of applying the preloading force. In the preferred embodiment the preloading mechanism is comprised of one or more springs which are retained by the seal housing and which apply the preloading force to the seal element to urge the seal engagement surface against the housing engagement surface.